(1) Field of the Invention
This invention relates to a platelet-increasing preparation comprising an interleukin-6 receptor, and a method of increasing platelets.
(2) Description of the Related Art
Interleukin-6 (abbreviated to "IL-6") is a lymphokine having an ability of increasing blood platelets. For example, it is reported in Ishibashi et al, Blood, vol. 74, p1241-1244 (1989) that administration of 5 .mu.g/d of human recombinant IL-6, produced by Escherichia coli, to mice for consecutive 5 days reproducibly elevated platelet counts by approximately 50% to 60% of increase. It is further reported in Asano et al, Blood, vol. 75, p1602-1605 (1990) that administration of 5 to 80 .mu.g/kg/d of the above human recombinant IL-6 to monkeys for consecutive 14 days caused dose-dependent increases in platelet count approximately twofold or more.
As seen from the above-cited reports, there is a demand of a method for increasing platelets by administration of human recombinant IL-6 and a platelet-increasing preparation comprising IL-6 as an effective ingredient, but a platelet-increasing preparation has not been developed yet at present.
IL-6 is bound to the surface of a target cell or to a soluble interleukin-6 receptor to stimulate gp130 protein on the target cell surface. Therefore, it is believed that, in order to increase platelet count by administration of human recombinant IL-6, it is essential that a certain number of IL-6 receptors are present on the surface of cell lines, which lead to production of platelets, such as multipotential stem cells or megakaryocytes, or a soluble IL-6 receptors are present at a certain concentration in blood or body fluid, whereby gp130 on the surface of cell lines is stimulated.
For example, in the case of human being, when a certain number of IL-6 receptors are not present on the surface of cell lines such as multipotential stem cells or megakaryocytes, and soluble IL-6 receptors are not present at a certain concentration in blood or body fluid, the platelet-increasing effect is not always obtained by administration of human IL-6, which is in contrast to the case of mice or monkeys.